THE USE OF SOIL CHEMISTRY, SOIL MORPHOLOGY, AND PARTICLE SIZE TO EXPLAIN STREAM WATER CHEMISTRY DIFFERENCES ACROSS A HEADWATER CATCHMENT IN THE SOUTHERN APPALACHIAN MOUNTAINS

Headwater streams play an important role in determining the water quality and ecological health of larger stream systems; however, controls on headwater stream chemistry are not well understood. This study investigated previously detected stream water chemistry differences between three main tributaries within the Gribble Gap catchment. Gribble Gap is 43 ha and is part of the Western North Carolina Hydrologic Research Station. This catchment has been disturbed from previous logging and use as pastureland. This study investigated the impact of soil properties on surface water chemistry. This was done by examining spatial variation in soil chemistry, particle size, and morphology. Variations in stream water chemistry have been documented between three tributaries in the study region, showing higher concentrations of exchangeable base ions (Si, Na, Ca) in northern tributaries than the southern tributaries within the catchment. Four soil pits were excavated and described (two in the north, two in the south). Soil samples were taken every 10 cm for particle size and elemental analysis. Particle size distributions were found using the MasterSizer 2000 and elemental analysis was carried out on digested samples on an ICP-OES. A dual phase mass balance (Tau parameter) was applied to assess weathering in the soil profiles. Soils in the south side (with lower stream water ion concentrations) of the catchment had more sand, and Tau values indicative of more weathering. Soils on the north side (with higher stream water ion concentrations) of the catchment had more clay, and Tau values indicative of less weathering. Soil profiles on the north have many horizons that change from dark to light colors from bottom to top, potentially indicating historical deposition. The assumption of deposition on the north side is supported by Tau values that indicate less weathering. Smaller particles are more chemically reactive, and slow the flow of water moving through the soils. The slow moving water through enriched soils would be expected to leach higher concentrations of ions into the stream system on the north side. These combined results suggest that the presumed deposition from past disturbance combined with spatial variation in weathering does play a role in determining the surface water chemistry throughout the Gribble Gap catchment.